1. Field of the Invention
The present invention relates to electroacoustic transducers for deep submersion. It relates in particular to axial transmission and/or reception transducers intended to operate in a marine environment at considerable depth e.g. deeper than 4,000 metres. Because of hydrostatic pressure it is difficult to produce such transducers for use at these depths.
2. The Prior Art
Various techniques are known at the present time for producing electroacoustic transducers which will operate when deeply submerged.
It is possible, for example, to use a gas to pressurise the interior of a sealed enclosure containing the transducer, the latter thus becoming capable of use at greater depths.
It is also possible to have a transducer which is submerged just as it is in the water and to shape the counter mass and front mass which contains its active face in such a way as to obtain the desired energy ratio between front and rear; also exists a submerged transducers termed "free flooded". Unfortunately it is impossible to obtain a Q factor of better than 6, which is a disadvantage for wide frequency band operation.
The transducer may be enclosed in a sealed cavity which is resistant to outside pressure. For this however it is necessary to use large amounts of a material which is extremely resistant to the compression stresses involved and ceramics made of a piezoelectric material which is of a particularly high standard from the mechanical point of view.
The interior of such a cavity may be made to communicate with the surrounding medium by means of a capillary passage passing through its walls, but the efficiency of the transducer is reduced due to energy losses resulting from residual radial-mode vibration.